Physics

• The word planet comes from the word "wanderer" in Greek.
• Aristarchus said that the sun was the center of the universe.
• Aristotle and Plato taught that earth was surrounded by four spheres.
• The geocentric idea proposed by Ptolemy was that the Earth was the center of the universe.
• Ptolemy explained the retrogade motion of the planetsby saying that planets go in smaller circles called epicycles.
• Nicolas Copernicus proposed the heliocentric model that was a sun-centered view.
• Johannes Kepler discovered three laws about planetary orbits based on observations made by Tycho Brahe.
• Kepler's first law states that all planets orbit around the Sun in an ellipse with the Sun at one focus.
• Galileo Galilei used his telescope to observe Jupiter's moons, which supported the heliocentric theory.
• Usualy it takes 100 years for a completely different idea to replace a common belief.
• The creator of the quadrant is Tycho Brahe, who was a Danish astronomer.
• Kepler's second law of motion was that planets go faster when they are closer to the sun and slower when they are farther from the Sun.
• The gravity causues the centripetal acceleration that keeps planets in orbit.
• Energy causes things to move.